Power presses are built in a wide variety of styles and sizes and those presses have a variety of applications, such as, forging, stamping, drawing, or other functions. A common construction of a power press is a double action press which combines the functions of blank holding with drawing. In many stamp and drawing operations, it has been found to be desirable to provide a die cushion which holds a blank to allow the metal of the blank to flow during working. A die cushion is often used to eject a worked blank. Die cushions come in various forms. A well known form is a rubber tankless type. Another well known form is a piston type which is an air cylinder assembly.
Die cushions utilizing an air cylinder assembly are generally a typical air cylinder construction having a cylinder and a piston movable relative to the cylinder. The construction of the air cylinder, as is conventional, utilizes various types of seals and packings to retain the air under pressure. The constant movement of the piston in the cylinder often results in wear in the seals and packing so that there is a constant loss of air from the cylinder, thereby causing the air to be wasted. The loss of air causes a needless operating cost in the operation of a press having an air cylinder die cushion. Importantly, the loss of air causes a variance in the holding force of the air cylinder resulting in a variance in the product produced by the press. In some instances, the variance causes some of the product to be unusable and thus be scrap.
The constant impact loading on a power press and die cushion causes wear to occur in the press and die cushion. It follows that it becomes necessary to maintain and repair the press as well as the die cushion. A desirable construction of a die cushion is one wherein the die cushion may be easily disassembled for maintenance or repair or the die cushion may be easily removed as a unit. Furthermore, it is desirable to provide a die cushion which has substantially no wear or air loss in operation.
In order to counterbalance the weight of the ram and its components and die members attached, and to take up the clearance in the main bearings and backlash in the gears thereto most presses are provided with a counterbalance. Traditionally the counterbalance utilized an air cylinder and piston as its major element. The constant movement of the piston in the cylinder often results in wear in the seals and packing utilized to retain the air under pressure, with the result that there is a constant loss of air from the cylinder. A typical construction for such a counterbalance is disclosed in U.S. Pat. No. 2,084,066, issued June 15, 1937, to F. J. Rode et al., entitled, "Metalworking Press". The Rode metalworking press utilizes a pneumatic cylinder embodying piston rods connected to pistons within cylinders to act as counterbalancing devices. The use of various additional systems for counterbalancing various presses is shown in the following patents: U.S. Pat. Nos. 1,970,134, issued Aug. 14, 1934, to W. Ferris, entitled, "Hydraulic Press"; 2,483,597, issued Oct. 4, 1949, to C. E. Schogren, entitled, "Supplemental Forging Press Die"; 3,115,676, issued Dec. 31, 1963, to O. F. Quartullo entitled, "High Speed Forging Apparatus"; 3,776,020, issued Dec. 4, 1973, to Fedosenko et al., entitled, "High-Speed Pressing Machine"; 3,834,216, issued Sept. 10, 1974, to Schiller et al, entitled, "Forging Press"; 3,914,975, issued Oct. 28, 1975, to Kawano, entitled, "Hydraulic Press Brake"; 4,148,209, issued Apr. 10, 1979, to Bessho, entitled, "Forging Press"; and 4,291,571, issued Sept. 29, 1981, to Claussen, entitled, "Forging Press". In addition, West German Auslegeshrift No. 1294 334, published May 8, 1969, discloses a cylinder construction for use with a press, as does USSR Publication Nos. 338034 and 1031617, of Sept. 15, 1981 and July 30, 1983, respectively.
Power presses are built in a wide variety of styles and sizes, and those presses have a variety of applications. In many applications, a press is used to operate at a high rate. The press moves quickly in its pressing stroke and moves at substantially the same rate in its return stroke. As is well known, die cushions are used as a work holding device or part ejector. The cushion which is used in certain instances includes a resilient bellows or actuator. The actuator receives a compressible fluid such as air, so that the lower portion of the die may travel a selected distance with the ram during the pressing operation.
Once the actuator of the cushion is compressed, and the ram starts its return stroke, the cushion moves the movable portion of the die with it, disengaging the workpiece. The die cushion actuator moves the movable portion of the die with a constant acceleration until the movable portion of the lower die is at its rest position. The lower portion of the die is provided with a stop which causes an abrupt halt to the movement of the die. This abrupt halt causes an impact loading on that portion of the die connected to the cushion and associated parts. The repeated impact loading on the parts of the die often causes damage to those parts.
It is desirable to provide a die cushion construction for use in a press wherein the stopping of the die is not an abrupt stop, but rather a substantially smooth stop, which reduces damage to the die by impact loading on the die. This construction also reduces damage to the press and the die cushion itself.
The object of this invention is to provide a power press with improved cushioning systems which do not require sliding seals to prevent the leakage of fluids from the system.
Another object is to provide a cushioning system which does not leak fluids from the system.
Another object is to provide a cushioning system which reduces shock, noise and excessive impact on the dies.
Another object is to provide a system which is more dependable and consistent in its operation and does not require lubrication.
Another object is to provide a system in which there are no variable frictional forces.
The present invention has for an object the slowing down of the die cushion during the final portion of its return stroke.
The invention has the further object of controlling the rate at which the cushion is stopped in its motion.
A further object is to provide a means by which the deceleration of the cushion may be varied during its stroke.
Another object is to provide a means whereby the cushion may be easily removed and replaced whenever maintenance service is required.
Another object is to provide a hydraulic snubber, to act in conjunction with a die cushion, which does not require any high pressure hydraulic seals in conjunction with its moving parts.
Another object is to provide cushioning systems which are less in weight and less in cost than piston type systems.
Another object is to provide cushioning systems which require very little maintenance.
Another object is to provide a cushion intensifier to increase the force holding the workpiece and vary the force while forming the workpiece during the downward motion of the ram.
Another object is to reduce the chance for parts to be misaligned in position or damaged when they are being separated from the fixed die after the drawing operation.
An ancillary object is to reduce the cost of die maintenance and to provide for a more consistent and uniform pressing operation.